A conventional accelerating apparatus of a carburetor is shown in FIG. 4.
Reference numeral 1 denotes a carburetor main body in which an intake passage 2 is provided so as to pass through. A lower opening portion 1a open downward is formed in a lower side of the intake passage 2, and a lower mounting collar portion 1b is formed in an outer periphery of a lower end of the lower opening portion 1a. 
The intake passage is provided so as to pass through from a front side toward a back side of a paper surface in FIG. 5, a venturi portion 2a where a diameter is most narrowed down is formed in an approximately intermediate portion of the intake passage 2, an intake passage 2b which is arranged in a downstream side from the venturi portion 2a is formed toward a front side from the venturi portion 2a, and an intake passage 2c which is arranged in an upstream side from the venturi portion 2a is formed toward a backside from the venturi portion 2a. 
Further, the intake passage 2c in the upstream side from the venturi portion is connected to an air cleaner (not shown), and the intake passage 2b in the downstream side from the venturi portion 2a is connected to an intake pipe of an engine (not shown).
Accordingly, clean air from which a foreign material is removed by the air cleaner flows to the intake passage 2c in the upstream side from the venturi portion 2a, the venturi portion 2a, and the intake passage 2b in the downstream side from the venturi portion 2a, and is supplied to the engine.
Further, a butterfly type throttle valve 3 is arranged within the intake passage 2b in the downstream side from the venturi portion 2a as shown in FIG. 5, and the throttle valve 3 is attached to a throttle valve shaft 4 which is rotatably supported to the carburetor main body 1.
Accordingly, the throttle valve 3 controls so as to open and close an opening area of the intake passage 2b in the downstream side from the venturi portion 2a on the basis of a rotational operation of the throttle valve shaft 4, whereby an amount of air supplied from the intake passage 2 toward the engine is controlled.
Further, a main fuel nozzle 5 and a main fuel jet 6 are arranged in a lower side of the intake passage 2, an upper end 5a of the main fuel nozzle 5 is arranged so as to protrude to the venturi portion 2a and is open therein, and a lower opening portion 6a of the main fuel jet 6 is arranged so as to be open downward.
Reference numeral 7 denotes a closed-end cup-shaped float chamber main body open upward. An upper mounting collar portion 7a is formed in an outer periphery of an upper end of the float chamber main body 7. A float chamber 8 is formed with a lower opening portion 1a of the carburetor main body 1 and an opening portion to an upper side of the float chamber main body 7, by bringing the upper mounting collar portion 7a of the float chamber main body 7 into contact with the lower mounting collar portion 1b of the carburetor main body 1 and fastening both by a screw.
Further, a fixed fuel liquid surface X—X is formed within the float chamber 8 on the basis of a cooperating effect of a float 9, a valve seat 11 arranged in an end portion of a fuel inflow path 10 connected to a fuel tank T, and a float valve 12 opening and closing the valve seat 11, as shown in FIG. 5.
In this case, the lower opening portion 6a of the main fuel jet 6 mentioned above is open below the fixed liquid surface X—X in the float chamber 8.
The opening portion 6a of the main fuel jet 6 is electrically opened and closed by a valve body V actuated by a solenoid apparatus S.
The solenoid apparatus S is provided with an electromagnetic coil 15 wound around a coil bobbin 14, a stationary core 16 fixed to a case 13, a movable core 17 movably arranged so as to oppose to the stationary core 16, and a spring 18 energizing the movable core 17 so as to move the movable core 17 apart from the stationary core 16, within a case 13.
Further, the valve body V is provided with a valve body Va opening and closing the opening portion 6A of the main fuel jet 6, and the valve body V is integrally formed with the movable core 17 so as to be synchronously moved with the movable core 17.
The solenoid apparatus is fixed by screw to an outer periphery of a lower side of the float chamber main body 7, and the valve body V passes through a bottom portion of the float chamber main body 7 and is opposed to the opening portion 6a of the main fuel jet 6.
A negative pressure actuation type accelerating apparatus P is formed in the following manner.
Reference symbol 7b denotes a pump chamber recess portion which is recessed toward a right side wall 7c of the float chamber main body 7, a partition body 20 constituted by a diaphragm is arranged in a right opening portion of the pump chamber recess portion 7b, a pressure receiving chamber cover 21 in which a pressure receiving chamber recess portion 21a formed in a closed-end cup shape is recessed is arranged on the partition body 20 so as to be brought into contact therewith, and the pressure receiving chamber cover 21 is fixed by a screw 22 toward the right side wall 7c of the float chamber main body 7 via the partition body 20 in this state.
In accordance with the structure mentioned above, a sealed pump chamber 23 is formed by a left side surface of the partition body 20 and the pump chamber recess portion 7b, and a sealed pressure receiving chamber 24 is formed by a right side surface of the partition body 20 and the pressure receiving chamber recess portion 21a. 
Further, an acceleration fuel intake path 25 connected to a portion below the fixed liquid surface X—X of the float chamber 8 is arranged to be open in the pump chamber 23, and an intake side check valve 26 allowing only a fuel flow from the float chamber 8 into the pump chamber 23 is arranged within the acceleration fuel intake path, in the pump chamber 23.
Further, an acceleration fuel discharge path 28 connected to the upstream side intake passage 2c from the venturi portion 2a via an accelerating nozzle 27 is arranged in the pump chamber 23 to be open therein, and a discharge side check valve 29 allowing only a fuel flow from the pump chamber 23 toward the accelerating nozzle 27 is arranged within the acceleration fuel discharging path 28.
On the other hand, a negative pressure introducing path 30a connected to an intake passage 2ba in a downstream side from the throttle valve 3 is arranged within the pressure receiving chamber 24 to be open therein, and a pump spring 31 is provided compressedly within the pressure receiving chamber 24, as shown in FIG. 5, and the partition body 20 is always energized to the side of the pump chamber 23 by spring force of the pump spring 31.
In accordance with the carburetor provided with the accelerating apparatus mentioned above, since no negative pressure is generated within the intake passage 2ba in the downstream side from the throttle valve 3 at a time when the engine stops, pressure within the pressure receiving chamber 24 is kept at approximately the atmospheric pressure, whereby the partition body 20 is pressed and held closest to the pump chamber 23 by the pump spring 31, so that a chamber volumetric capacity of the pump chamber 23 is kept small. (This state is shown in FIG. 4.)
Next, when an ignition switch (not shown) is closed, and a start operation of the engine is executed, the throttle valve 3 is held at a low opening degree at the starting time mentioned above, whereby great negative pressure is generated within the intake passage 2ba in the downstream side from the throttle valve 3, and the negative pressure is introduced into the pressure receiving chamber 24 via the negative pressure introducing path 30a. 
In accordance with the structure mentioned above, the partition body 20 moves to a side of the pressure receiving chamber 24 against a spring force of the pump spring 31 so as to increase the chamber volumetric capacity within the pump chamber 23. Accordingly, great negative pressure is generated within the pump chamber 23, the intake side check valve 26 opens the acceleration fuel intake path 25 as well as the discharge side check valve 29 closes the acceleration fuel discharge path 28, and fuel within the float chamber 8 is sucked and held within the pump chamber 23 via the acceleration fuel intake path 25.
Further, since the throttle valve 3 is opened from a low opening degree state toward middle and high opening degrees at a time of the engine accelerating operation in which the throttle valve 3 is opened from the low opening degree state toward the middle and high opening degree states, negative pressure in the downstream side from the throttle valve 3 is lowered (the lowering of the negative pressure means that the pressure comes close to the atmospheric pressure), the lowered smaller negative pressure is introduced into the pressure receiving chamber 24 via the negative pressure introducing path 30a, and negative pressure within the pressure receiving chamber 24 becomes small.
In accordance with the structure mentioned above, the partition body 20 moves to the side of the pump chamber 23 by the spring force of the pump spring 31, and reduces the chamber volumetric capacity of the pump chamber 23.
In accordance with the reduction of the chamber volumetric capacity in the pump chamber 23, the inside of the pump chamber 23 is pressurized, and pressure within the pump chamber 23 is increased. Further, the discharge side check valve 29 opens the acceleration fuel discharge path 28 as well as the intake side check valve 26 closes the acceleration fuel intake path 25, pressure of the fuel stored and held within the pump chamber 23 is increased, and the acceleration fuel is injected and supplied toward the inside of the intake passage 2c in the upstream side from the venturi portion 2a via the acceleration fuel discharge path 28 and the accelerating nozzle 27, whereby it is possible to achieve an improved accelerating operation of the engine.
Paying attention to the solenoid apparatus S provided with the valve body V, when the ignition switch is closed and the start operation of the engine is executed, the electromagnetic coil 15 is electrified, and the movable core 17 is attracted toward the stationary core 16 against spring force of the spring 18. Accordingly, the valve body V integrally formed with the movable core 17 moves downward in FIG. 4, and the valve portion Va opens the opening portion 6a of the main fuel jet 6. The opening of the opening portion 6a by the valve portion Va is continuously executed during the operation of the engine.
Accordingly, an improved engine operation can be achieved without preventing fuel flow from the fuel jet 6 toward the main fuel nozzle S during the operation of the engine.
On the other hand, when opening the ignition switch so as to stop the engine, the engine rotates on the basis of an inertia rotation, and the rotating speed is gradually lowered and stops after a certain time passes.
Further, the throttle valve 3 automatically opens the intake passage on the basis of a governor mechanism provided in the engine (the governor mechanism and the throttle valve shaft 4 of the carburetor are connected via a governor rod, and the governor mechanism and the governor rod are not illustrated).
In accordance with the matter that the throttle valve 3 is automatically opened by the governor mechanism and the engine rotates by inertia although being at the low rotation speed, just after the engine stops as mentioned above, air flow is generated within the intake passage 2, negative pressure is generated in the venturi portion 2a, and fuel within the float chamber 8 is going to be sucked out from the upper end 5a of the main fuel nozzle 5 into the venturi portion 2a via the main fuel jet 6 on the basis of the negative pressure.
However, in the solenoid apparatus S, since electric current supply to the electromagnetic coil 15 of the solenoid apparatus S is shut off at the same time when the ignition switch is opened so as to stop the engine, the opening portion 6a of the main fuel jet 6 is immediately closed by the valve portion Va of the valve body V, and fuel within the float chamber 8 is inhibited from flowing toward the main fuel jet 6 and the main fuel nozzle 5.
Accordingly, even if negative pressure is generated in the venturi portion 2a in the structure mentioned above, fuel is not sucked out toward the inside of the venturi portion 2a from the upper end of the main fuel nozzle 5, whereby it is possible to inhibit an after burn phenomenon that unburned fuel reaches an exhaust pipe and is ignited within the exhaust pipe from being generated.